Writing Regular Expressions
A regular expression is a precise pattern that provides a very efficient way to specify and recognize strings of text. A combination of various characters along with the text to be searched for generates a regular expression.
TallyPrime Developer uses regular expression to search for text based on specified patterns. These patterns are a combination of special characters and the text that needs to be searched for.
Some examples are given in the table below:
|
Character |
Description |
Example |
|
^ |
Used to match the start of a line |
^Local This expression will search for all lines that start with Local |
|
$ |
Used to match the end of a line |
$Tally This expression will search for all lines that end with Tally |
|
. |
Used to match or replace a Single Character |
F.rm This expression will search for all terms which start with F, have one character in the middle and end with rm |
|
* |
Searches for zero or more occurrences of the preceding character |
Lo*cal This expression will search for Lcal, Local, Loocal, Looocal… |
|
+ |
Searches for one or more occurrences of the preceding character |
Lo+cal This expression will search for all terms Local, Loocal, Looocal….. |
|
\x |
Used to search for a character which otherwise may have another meaning |
\ This expression will search for locations where ‘[‘ is present. |
|
\< |
Used to match the start of a word |
\<Ad This expression will search for all terms that begin with Ad |
|
\> |
Used to match the end of a word
|
\>ed This expression is used for all terms that end with ed |
|
\( |
Used to denote the start of a region for tagging a match |
|
|
\) |
Used to denote the end of a region for tagging a match |
|
| […..] |
Denotes a set of possible character matches |
[A-z]
It will search for terms with characters between a to z |
| [^…] |
Used to indicate complement of a set of characters |
[^A-d]
lt will not search for terms with characters between a to d |
|
\d |
Used to match a digit |
Tally\(\d+\) It will search for terms with a combination of text and numbers like Tally1, Tally512 |
|
\s |
Used to match a white space character |
Tally\s It will search for terms with Tally and a line feed character after it like space or tab |
Combination of Characters
To make a search more refined, we use a combination of characters. Any of the characters given above can be used in conjunction with each other to get a thoroughly enhanced output. Given below are a few examples to explain how this can be done.
|
Regular Expression |
Result |
|
^Tally\([abc]\) |
This will search for terms which start at the beginning of the line and consist of Tallya, Tallyb or Tallyc. |
|
Tal*y\(\d+\) |
This will search for terms which have zero or more occurrences of l between a and y and any digits after the text. |
|
^.$ |
This will search for lines containing only a single character. |
|
^Pa? |
This will search for any term which has a P OR Pa at the beginning of the line. |
From the above examples we can see that regular expression is the term used to describe a codified method of searching which enables fast and responsive searches.
